Mobile object identification system

ABSTRACT

The primary object of the invention is to realize a mobile object identification system of simple construction and low cost, in which the responding unit attached to a mobile object writes data only once when it receives write signals repeatedly in communication with antenna units. When a tag unit (responding unit) receives a write signal from a writing antenna unit, it writes data to the data memory when a completion flag is cleared. When the data is first written, a control circuit sets the completion flag. Then, if the tag unit receives additional write signals in the communication area of the same writing antenna unit, the control circuit invalidates the data write command on the ground that the completion flag is set, thereby preventing duplicate data writing.

FIELD OF THE INVENTION

The present invention relates to a mobile object identification systemfor identifying a responder mounted on a mobile object in acommunication area by transmitting interrogatory signals from aninterrogator to the responder and receiving responding signals from theresponder.

BACKGROUND OF THE INVENTION

A mobile object identification system transmits interrogatory signalsfrom an interrogator to a responder attached to a mobile object andreceives responding signals from the responder, thereby identifying theresponder. Recently, there has been demand for mobile objectidentification systems that can assure accurate communication betweeninterrogator and responder.

BRIEF SUMMARY OF THE INVENTION

To meet this demand, the first object of the invention (first invention)is to provide a responder for a mobile object identification systemthat, in the communication area of a writing interrogator, can writedata upon receipt of a write signal and that, in the communication rangeof a reading interrogator, can read and transmit necessary data uponreceipt of a read signal as it moves with the mobile object. Theresponder according to this invention comprises: data storage means forwriting or reading necessary data; control means for controlling theprocessing for writing data to or reading data from the data storagemeans; and status storage means for storing the write completion statuswhen necessary data has been written to the data storage means undercontrol of the control means, so as to respond to a write signalreceived from the writing interrogator. The control means invalidatesthe processing for writing data when, with the write completion statusretained in the status storage means, it receives a write signal fromthe writing interrogator.

According to the first invention, when the responder of the mobileobject identification system receives a first write signal in thecommunication area of the writing interrogator, the control means writesthe necessary data to data storage, and the status storage means ensuresstorage of the write completion status data. In this state, if theresponder receives a second write signal from the writing interrogator,the control means invalidates the signal, since the write completionstatus data is already stored.

For various reasons, the mobile object may move slowly or stop in thecommunication area of the writing interrogator. In such a case, theresponder attached to the mobile object receives the write signalrepetitively from the writing interrogator. With the responder of thefirst invention, since the control means invalidates processing forwriting the second and subsequent write signals, it allows a writesignal to be written only once. Even if a plurality of responders arepositioned in the same communication area, each responder operates asdescribed above so that a write signal is written only once in eachresponder.

The second object of the invention (second invention) is to provide amobile object identification system communication complex comprising: aresponder for transmitting/receiving signals through the mobile antennamounted on a mobile object; an interrogator for transmitting/receivingsignal through a plurality of stationary antennas installed along themoving area of the mobile object; and a control device for controllingoperation of the interrogator. The interrogator includes a level judgingcircuit to identify the highest-level responding signal of thosereceived by the stationary antennas, and a signal selection circuit toselectively output to the control device the responding signalidentified by the level judging circuit.

According to the communication complex of the second invention, theinterrogator transmits interrogatory signals through the antennas. Whenthe mobile object enters the communication area, the responder mountedon the mobile object transmits a responding signal in response to theinterrogatory signal received.

Since the interrogator has the plurality of antennas installed along themoving area of the mobile object, the responder communicates with theplurality of antennas simultaneously. The level judging circuit of theinterrogator identifies the highest-level responding signal of all thesignals received by these antennas, and the level selection circuitselectively outputs to the control device the responding signalidentified by the level judging circuit, enabling the control device toread the highest-level responding signal without switching antennas.

The third object of the invention (third invention) is to provide amobile object identification system comprising a responder mounted on amobile object, which responder, when receiving an interrogatory signalin a specified frequency band, with a responding signal, modulates theunmodulated carrier wave received after the interrogatory signal, andtransmits the responding signal-modulated carrier wave. Each of aplurality of interrogators modulate, with the interrogatory signal, thecarrier wave in the specified frequency band allocated for each of thecommunication areas of the plurality of interrogators, transmit theinterrogatory signal-modulated carrier wave, followed by unmodulatedcarrier wave, to the appropriate communication area. Each interrogatoralso receives the responding signal from the responder positioned in theappropriate communication area. A control means controls the pluralityof interrogators so that at least those interrogators whosecommunication areas overlap transmit carrier waves in differentfrequency bands and transmit interrogatory signals at different timings.

According to the mobile object identification system of the thirdinvention, when the responder mounted on the mobile object is in any oneof the plurality of communication areas provided by the plurality ofinterrogators, the appropriate interrogator transmits the interrogatorysignal; the responder receives the interrogatory signal, generating aresponding signal in response. The carrier wave received after theinterrogatory signal is then modulated by the responding signal, and theresponder transmits the responding signal-modulated carrier wave. Theinterrogator receives this wave, thereby identifying the respondingsignal.

When the responder is located in the zone where communication areasoverlap, the corresponding interrogators transmit interrogatory signalsat different frequencies and different timings via the control means, sothat the responder receives one interrogatory signal from any of theinterrogators at a time. Thus, the responder accepts the interrogatorysignal received first, generates a responding signal which modulates thecarrier wave received after the interrogatory signal, and transmits theresponding signal-modulated carrier wave.

At this time, it is possible that the responding signal-modulatedcarrier wave is received by the two interrogators whose communicationareas overlap the appropriate one. Even in such a case, the respondercan communicate with the appropriate interrogator without radiointerference, due to the difference in frequency of the respondingsignal-modulated carrier wave from the frequency allocated for the otherinterrogator. In addition, according to the present invention, unlike inconventional cases, where the communication period is time-shared bymultiple interrogators, radio waves can be transmitted simultaneously inthe zone where communication areas overlap. Consequently, the respondermounted on the mobile object can communicate with an appropriateinterrogator promptly and accurately, even when moving at high speed.

The fourth object of the invention (fourth invention) is to provide anelectronic label for the mobile object identification system comprising:a responding circuit in which is stored vehicle information such as theframe number (e.g., vehicle identification number (VIN)), and whichoutputs the vehicle information in response to an interrogatory signalreceived from an interrogator. Information given on the surface of theelectronic label is that found on such labels that are legally requiredto be attached to a vehicle.

When an interrogatory signal is sent from an external interrogator tothe vehicle to which the electronic label of the fourth invention isattached, the responding circuit receives the interrogatory signal, andreturns the preliminarily loaded vehicle information. Therefore, thevehicle information need not be checked visually. Even if the vehicle isoften running past without stopping, the vehicle information can berecognized easily.

When the electronic label bears on the surface the same particulars asgiven on a mandatory vehicle inspection label or a regular check andmaintenance label legally attached to the windshield glass of thevehicle, the electronic label can be attached to the windshield glasswithout causing any problems. This position is also the optimum forelectronic label reception of interrogatory signals transmitted fromahead of or above the vehicle. For a vehicle to be driven on publicroads, it is legally required to have such vehicle inspection label orregular check and maintenance label attached. Therefore, such a label isnot to be removed. Accordingly, the information read from the electroniclabel attached to the windshield glass of a vehicle can be considered asinformation specific to the vehicle.

The fifth object of the invention (fifth invention) is to provideanother electronic label for the mobile object identification systemcomprising: a responding circuit in which is stored vehicle informationsuch as the frame number and which outputs the vehicle information inresponse to an interrogatory signal received from an interrogator, theresponding circuit being embedded in the windshield or window glass.

When an interrogatory signal is sent from an external interrogator to avehicle equipped with the electronic label of the fifth invention, theresponding circuit embedded in the window glass receives theinterrogatory signal and returns the preliminarily written vehicleinformation. Therefore, as with the fourth invention, the vehicleinformation need not be checked visually, and can be recognized easilyif the vehicle is running past without stopping.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of the control program for an embodiment of theresponder according to the first invention;

FIG. 2 is a schematic view explaining the general concept of the firstinvention;

FIG. 3 is a block diagram showing the electrical construction of thefirst invention;

FIG. 4 is a schematic view explaining conventional art as opposed to thefirst invention;

FIG. 5 is a schematic view explaining another conventional device asopposed to the first invention;

FIG. 6 is a schematic view explaining the disadvantages of theconventional art as opposed to the first invention;

FIG. 7 is a block diagram showing the construction of the interrogatorused in an embodiment of the communication complex according to thesecond invention;

FIG. 8 is a block diagram of the responder used in the second invention;

FIG. 9 is a schematic view explaining the general concept of the secondinvention;

FIGS. 10A to 10C are a chart showing change in signal level of theresponding signals by the second invention as a mobile object is moving;

FIG. 11 is a schematic view explaining the general concept of the mobileobject identification system according to the third invention;

FIG. 12 is a perspective view showing the general appearance of thethird invention;

FIG. 13 is a block diagram showing the electrical construction of thethird invention;

FIG. 14 is a chart showing the frequency characteristics of theinterrogator and responder of the third invention;

FIGS. 15A to 15E are a timing chart of interrogatory signal outputs ofthe third invention;

FIG. 16 is a schematic view explaining an operation of the thirdinvention;

FIG. 17 is a schematic view explaining another operation of the thirdinvention;

FIG. 18 is a schematic view explaining the disadvantage of conventionalart as opposed to the third invention;

FIG. 19 is a schematic view explaining the disadvantage of anotherconventional device as opposed to the third invention;

FIG. 20 is a general perspective view showing an embodiment of theelectronic label according to the fourth invention;

FIG. 21 is a perspective view showing an example of the actualapplication of the fourth invention;

FIG. 22 is a diagram showing the electrical construction of theresponding circuit of the fourth invention;

FIG. 23 is an electric circuit diagram of the interrogator for thefourth invention;

FIG. 24 is a schematic view explaining an example of the actualapplication of the fourth invention to a toll road accounting system;

FIG. 25 is a schematic view explaining an example of actual applicationof the fourth invention to an incoming/outgoing vehicle managementsystem of a parking lot;

FIG. 26 is a schematic view explaining an example of the actualapplication of the fourth invention to a regular customer sensingsystem;

FIG. 27 is a general view of the windshield glass of a vehicleincorporating the responding circuit of the electronic label of thefifth invention, as viewed from inside the vehicle;

FIG. 28 is a schematic view showing the general construction of theresponding circuit of the fifth invention;

FIG. 29 is a general view of the windshield glass of a vehicleincorporating the responding circuit of the fifth invention connected toanother information processor, as viewed from inside the vehicle;

FIGS. 30A to 30C are sectional views of window glass for explaining themethod of embedding the responding circuit of the fifth invention in thewindow glass;

FIG. 31 is a diagram showing the general electrical construction ofanother embodiment of the fifth invention, concerning the window glassthat incorporates the responding circuit;

FIG. 32 is a general view of the windshield glass of a vehicleincorporating the responding circuit of the second embodiment of thefifth invention, as viewed from inside the vehicle; and

FIG. 33 is a circuit diagram for explaining the memory in the RFprocessing IC of the information processor.

BEST MODE FOR CARRYING OUT THE INVENTION

Prior to explaining the first invention, the conventional art as opposedto the first invention and its problems will be described in detail inthe following.

A mobile object identification system has many applications, one ofwhich is in the system for managing unmanned trucks in a factory. Thissystem comprises a tag unit mounted as a responding unit on eachunmanned truck, and antenna units installed along the passage ofunmanned trucks to provide communication areas for communication withtag units. Each tag unit of this system includes a memory for storingvarious data, such as the identification code, quantities anddestinations of the articles being transported by the unmanned truck.This memory is designed to enable readout of stored data and write-in ofnew data, as necessary.

Each antenna unit is designed to transmit a carrier wave of specifiedfrequency as modulated by an interrogatory signal, and then anunmodulated carrier wave to its communication area. As an unmanned truckmoves, the tag unit attached to the truck enters a communication areaand receives an interrogatory signal. The tag unit then generates aresponding signal containing various data such as article identificationcode, to answer the interrogatory signal, via a responding signal,modulates the unmodulated carrier wave received following theinterrogatory signal, and transmits the responding signal-modulatedcarrier.

The antenna unit receives the responding signal, by which it identifiesthe tag unit of the unmanned truck passing through the communicationarea, and recognizes the articles being carried by the truck. Accordingto this information, the antenna unit stores new data and/or controlsthe operation of the unmanned truck, as necessary.

Some of such conventional mobile object identification systems use adata memory composed of nonvolatile memory such as EEPROM, for theresponding unit. Generally, a significant amount of time is needed towrite data to a nonvolatile memory. When the interrogatory signal froman antenna unit includes a data write command, therefore, the processingfor writing data to the data memory takes an extended time. When theunmanned truck is moving at a high speed, the tag unit could thereforepass through the communication area before it can read data written toits data memory and send it to the interrogating unit, thus hamperingaccurate communication.

One conventional device attempts to solve this problem with a mobileobject identification system in which an antenna unit is divided into awriting antenna unit 10A and a reading antenna unit 12A, which arearranged in that order along the passage 16A of an unmanned truck 14A,as illustrated in FIG. 4. The writing antenna unit 10A transmits writesignals to the unmanned truck 14A in the communication area 18A, and thereading antenna unit 12A, installed at a downstream position, transmitsread signals the unmanned truck 14A in the communication area 20A.Therefore, if the tag unit 22A, attached to the unmanned truck 14A,takes time in writing data to its data memory, tag unit 22A can completethe processing for writing data before it enters the communication area20A of the reading antenna unit 12A. In other words, if the unmannedtruck 14A is moving at a high speed, the system can identify the truckthrough accurate communication between the tag unit and antenna units.

However, this conventional art also has a drawback. The unmanned truck14A may stop in the communication area 18A of the writing antenna unit10A for a certain reason. In such a case, the tag unit 22A attached tothe unmanned truck 14A repeatedly receives a write signal transmittedfrom the writing antenna unit 10A. If the write signal includes a writecommand for such data as the number of transits, the number of transitswill be written and updated every time the write signal is received.Consequently, the wrong number of transits is stored in the tag unit22A.

The system shown in FIG. 5 solves this problem. According to thisarrangement, object detectors 24Aa, 24Ab, 26Aa and 26Ab are installedbefore and after the antenna units 10A and 12A, respectively, to detectan object. That is, these detectors detect the tag unit 22A if it is inthe communication area 18A or 20A of the antenna unit 10A or 12A. Withthis arrangement, the system calculates that the unmanned truck 14Aexists in the communication area 18A or 20A for the period from the timewhen it is detected by the object detector 24Aa or 26Aa to the time whenit is detected by the object detector 24Ab or 26Ab. Therefore, thesystem with this arrangement can solve the above-mentioned problem bycontrolling antenna unit 10A or 12A to transmit a write signal onlyonce, when the unmanned truck 14A enters and stays in the communicationarea 18A or 20A.

This arrangement, however, also has a drawback. There is no problem aslong as unmanned trucks 14A with tag units 22A pass one by one throughthe communication area 18A or 20A. However, two unmanned trucks 14A maypass through the communication area 18A or 20A simultaneously, as shownin FIG. 6. In such a case, since the antenna unit 10A or 12A iscontrolled to transmit a write signal only once, it transmits a writesignal to the tag unit 22A entering the communication area 18A or 20Afirst, but not to the tag units 22A entering the communication arealater.

If the antenna unit 10A or 12A transmits a write signal two times whenthe object detector 24Aa or 26Aa detects two unmanned trucks 14A in thecommunication area 18A or 20A, the tag unit 22A entering thecommunication area first will receive the write signal two times,resulting in duplicate writing.

The first invention has solved the above-mentioned problems of theconventional arts. An embodiment of the first invention is described indetail with reference to FIGS. 1 through 3 below. In this embodiment,the first invention is applied to a tag unit for use in thecommunication system for unmanned trucks.

In FIG. 2, that shows the general concept of the first invention, anunmanned truck 30A as a mobile object is controlled by a control device(not shown) to move along a passage 32A. The truck 30A loaded witharticles is expected to run along the passage 32A in the direction ofarrows toward a specified destination.

A writing antenna unit 36A providing a communication area 34A, and areading antenna unit 40A providing a communication area 38A areinstalled in that order at specified adjacent positions along thepassage 32A. A writing antenna unit 44A providing a communication area42A and a reading antenna unit 48A providing a communication area 46Aare also installed in that order at specified adjacent positions alongthe passage 32A downstream from the antenna units 36A and 40A.Accordingly, when the unmanned truck 30A runs along the passage 32A, itpasses through the communication areas 34A, 38A, 42A and 46A in thatorder.

The unmanned truck 30A is provided with a tag unit 50A as a responder ofthe present invention, so that it communicates with the antenna units36A, 40A, 44A and 48A in the communication areas 34A, 38A, 42A and 46A,respectively, as will be described later.

Each of the antenna units 36A, 40A, 44A and 48A comprises batch antennasrealized by microstrip lines formed on PC boards; these batch antennasare arranged in multiple groupings as an array antenna to improve thedirectivity and to accommodate long-distance communication. To transmitwrite/read signals, the antenna units 36A, 40A, 44A and 48A usesemi-microwaves in a frequency band of, for instance, 2.45 GHz ascarrier waves.

The antenna units 36A, 40A, 44A and 48A transmit the above-mentionedcarrier waves as modulated by a write/read signal during the write/readsignal transmission period, and transmit unmodulated carrier wavesduring the other period. While the antenna unit 36A, 40A, 44A or 48A istransmitting an unmodulated carrier wave, it receives radio waves sentfrom the tag unit 50A in the communication area 34A, 38A, 42A or 46A.

FIG. 3 shows the electrical construction of the tag unit 50A, a controlcircuit 52A includes a CPU, ROM and RAM as control means. The controlcircuit 52A stores a control program (described later) for controllingcommunication as well as for use as a status storage means (alsodescribed later). An antenna 54A is composed of, for example, batchantennas realized by microstrip lines formed on PC boards.

The antenna 54A is connected to the control circuit 52A in two ways:through a radio wave detector 56A and through a demodulation circuit58A. The antenna 54A is grounded via a switch circuit 60A. The controlpin of the switch circuit 60A is connected to the control circuit 52Athrough a modulation circuit 62A. The radio wave detector 56A detectsthe radio wave received by the antenna 54A, and outputs the detectiondata to the control circuit 52A. The demodulation circuit 58Ademodulates the radio wave received by the antenna 54A, and outputs thedemodulated wave as a reception signal to the control circuit 52A. Themodulation circuit 62A modulates the carrier wave by opening/closing theswitch circuit 60A according to the responding signal output from thecontrol circuit 52A.

A data memory 64A connected to the control circuit 52A forms datastorage means. The data memory 64A is composed of a nonvolatile memorysuch as an EEPROM. The control circuit 52A executes the processing forwriting or reading various data into or out of the data memory 64A asrequired. All these circuits of the tag unit 50A are fed with power by abattery (not shown).

The operation of this embodiment of the first invention is describedwith reference to the flow chart of FIG. 1. When power is supplied, thecontrol circuit 52A of the tag unit 50A starts running the communicationcontrol program shown in FIG. 1. Specifically, after initialization(step S1), the control circuit 52A is put in the wait state until itreceives a radio wave in step S2. In the above initialization step,various registers and flags are cleared for initial setting. Thecompletion flag F, as the status storage means, is also cleared in stepS1 (F←0).

When the unmanned truck 30A moves into the communication area 34A of thewriting antenna unit 36A, the antenna 54A of the tag unit 50A receives awrite signal transmitted from the writing antenna unit 36A. The radiowave detector 56A detects this write signal, and outputs a detectionsignal to the control circuit 52A. Based on the detection signal, acontrol circuit 52A makes a judgment of "YES" in step S2, and advancesthe program to step S3, to check if the radio wave received is a writesignal. Since the control circuit 52A receives a reception signal asopposed to the write signal from the demodulation circuit 58A, it makesthe judgment for "YES" in step S3, and advances the program to step S4.

In step S4, the control circuit 52A checks if the completion flag F hasbeen set. Since the completion flag F has not yet been set (F=0), thecontrol circuit 52A makes a judgment of "NO", and advances the programto step S5 where necessary data is written to the data memory 64A. Then,after setting the completion flag F (F←1) in step S6, the programreturns to step S2.

The data writing process in step S5 takes longer than other processing.Therefore, if the unmanned truck 30A is moving at ordinary speed, thetag unit 50A may complete data writing by the time the unmanned truck30A leaves the communication area 34A of the writing antenna unit 36A.

If the unmanned truck 30A is moving at low speed, the tag unit 50A maystill be in the communication area 34A of the writing antenna unit 36Awhen it has completed data writing. In such a case, the tag unit 50Areceives a write signal again. However, when the program proceedsthrough steps S2 and S3 to step S4, the control circuit 52A makes thejudgment of "NO" because the completion flag F has already been set(F=1), and the program is advanced to step S7. In step S7, since thewrite signal received the second time is transmitted from the samewriting antenna unit that sent the first write signal, the controlcircuit 52A makes the judgment of "YES," and the program returns to stepS2. In other words, since data writing is already executed, the controlcircuit 52A invalidates the second or subsequent write data.

When the unmanned truck 30A enters the communication area 38A of thereading antenna unit 40A, the tag unit 50A operates as follows. Thecontrol circuit 52A runs the program through step S2 to step S3 in thesame procedure as already described, makes the judgment of "NO", andadvances the program to step S8. Since the control circuit 52A hasreceived a read signal from the demodulation circuit 58A, it makes thejudgment of "YES" in step S8. The program is advanced to the step S9where the control circuit 52A carries out the data reading process.After the completion flag F is cleared (F←0) in step S10, the programreturns to step S2.

By the data reading process in step S9, the control circuit 52A reads tocheck data recorded, for example, by the write processing in the datamemory 64A, for transmission to the reading antenna unit 40A. Totransmit the data thus read, the control circuit 52A sends it as aresponding signal to the modulation circuit 62A, which carries outmodulation using the responding signal, and controls the ON/OFF state ofthe switch circuit 60A.

The unmodulated carrier wave sent from the reading antenna unit 40A andreceived by the antenna 54A is thus reflected or absorbed, andtransmitted back to the reading antenna unit 40A. The reading antennaunit 40A receives the radio wave transmitted from the communication area38A while it is sending an unmodulated carrier wave. The radio wave thusreceived is demodulated to obtain a responding signal.

In step S8, if the radio wave received by the antenna 54A is neither awrite signal nor a read signal, the control circuit 52A makes thejudgment of "NO," assuming that the radio wave is transmitted from asource other than the antenna unit 36A or 40A. The program then returnsto the step S2.

If the unmanned truck 30A stops in the communication area 34A of thewriting antenna unit 36A for some reason, the tag unit 50A will receivea write signal repeatedly. According to the present invention, once thecontrol circuit 52A has carried out the data writing process, itinvalidates the second and subsequent write signals, and does notconduct data writing any more. Therefore, the problem of duplicate datawriting does not occur.

If more than one unmanned truck 30A are positioned in the communicationarea 34A each, receiving a write signal repeatedly from the writingantenna unit 36A, the tag unit 50A of each unmanned truck 30A carriesout the data writing process only once, due to the above-mentioned meansof the control circuit 52A.

According to the present invention, the unmanned truck 30A is controlledto pass through the communication area 34A of the writing antenna unit36A prior to the communication area 38A of the reading antenna unit 40A.Normally, therefore, as the unmanned truck 30A runs through the passageand moves out of the communication area 38A, the completion flag F isset in step S6 and cleared in step S10 by the control circuit 52A.Accordingly, when the unmanned truck 30A enters the communication area42A of another writing antenna unit 44A, the tag unit 50A carries outthe data writing process only once.

However, if more than one unmanned truck 30A are running in parallelthrough, for example, the communication area 38A of the reading antennaunit 40A, it is possible that the tag unit 50A of a truck behind theother truck does not receive a read signal sent from the reading antennaunit 40A.

When the unmanned truck 30A that has received a read signal in thecommunication area 38A enters the communication area 42A of the writingantenna unit 44A and receives a write signal there, the control circuit52A of the tag unit 50A carries out the data writing process as follows.The program is advanced through steps S2 and S3 to step S4. Since thecompletion flag F is not cleared (F=1), the control circuit 52A makesthe judgment of "YES" in step S4, and advances the program to step S7.Since the tag unit 50A receives a write signal from the writing antennaunit 44A and not from the writing antenna unit 36A, the control circuit52A makes the judgment of "NO" in step S7 and advances the program tostep S5 where data is written.

Thus, according to this invention, when the tag unit 50A receives awrite signal from the writing antenna unit 36A or 44A, the controlcircuit 52A executes a data writing process, and sets the completionflag F to invalidate any write process by the second or subsequent writesignal, thereby preventing duplicate data writing to the data memory64A. Even if more than one tag unit 50A exist in the communication area34A or 42A, each tag unit 50A carries out the data writing process onlyonce.

In addition, according to the present invention, the control circuit 52Achecks in step S7 if the write signal received has been sent from thesame writing antenna unit as the last write signal, and writes data ifit makes the judgment of "NO". Therefore, even if the tag unit 50A hasnot received a read signal from the reading antenna unit 40A or 48A, itcan write data without fail when it receives a write signal.

In the above-mentioned embodiment of the first invention, the datamemory 64A uses an EEPROM as data storage. A battery-backup RAM or othermemory, such as a so-called IC card, can be used instead of the EEPROMwithout departing from the spirit of the present invention.

In the above embodiment, the invention is applied to the tag unit forthe system of identifying unmanned trucks. The invention is alsoapplicable to the responding unit of any other mobile objectidentification system. For example, it may be applied to the tag unitfor the process control system in a factory to control production byattaching the tag unit to each product in the line. It is alsoapplicable to the ID card for a system of managing personsentering/exiting a room.

Now, prior to explaining the second invention, the conventional art asopposed to the second invention and its problems will be described indetail in the following.

various communication complexes have been in operation for mobile objectidentification systems. A typical example is a complex in which aninterrogator transmits an interrogatory signal to communicate with aresponder attached to each product being carried on a conveyor line,receives a responding signal sent from the responder, and outputs it toa control device for data processing.

In particular, the interrogator sends an interrogatory signal through anantenna. When a mobile object enters the communication area, theresponder attached to the mobile object receives the interrogatorysignal through an antenna, and transmits a signal in response to theinterrogatory signal. The interrogator receives the responding signaland outputs it to the control device which processes the respondingsignal, and sends the processed data to a host computer when necessary.

Recently, the quantity of communication data to be handled by such acommunication system has been expanding with the increase in operatingspeed of conveyor lines, causing communication time shortage.Conventionally, this problem is overcome by installing multiple antennasof the interrogator along the moving passage of products and outputtinga responding signal from each of the antennas to the control device. Thecontrol device selects the antenna receiving the highest levelresponding signal.

With the above-mentioned conventional method, however, the controldevice is required to switch antennas while reading the respondingsignals output from the interrogator. During the antenna switchingperiod, the control device cannot read a responding signal, so datacommunication is interrupted.

The second invention has solved the above-mentioned problems of theconventional art. An embodiment of the second invention will bedescribed in detail below.

FIG. 9, that shows the general concept of the second invention. Aninterrogator 10B has a first stationary antenna 12B and a secondstationary antenna 14B, and transmits interrogatory signals selectivelythrough the first and second stationary antennas 12B and 14B. Aresponder 18B is attached to a mobile object 16B. The first and secondstationary antennas 12B and 14B are installed along the moving area ofthe mobile object 16B. The communication area of each of the stationaryantennas 12B and 14B is indicated by the chain double-dashed line. Theinterrogator 10B can communicate with the responder 18B when the mobileobject 16B is positioned in either of the communication areas.

The communication areas of the first and second stationary antennas 12Band 14B overlap. The interrogator 10B is designed to transmitinterrogatory signals as controlled by a control device 20B, and tooutput responding signals received from the responder 18B to the controldevice 20B.

FIG. 7 shows the construction of the interrogator 10B, the interrogator10B is connected to the control device 20B through an input pin 10Ba andan output pin 10Bb. The interrogator 10B comprises a level judgingcircuit 22B, a signal selection circuit 24B and a demodulator 26B inaddition to the first and second stationary antennas 12B and 14B.

Since the first and second stationary antennas 12B and 14B are of thesame construction, the first stationary antenna 12B alone will bedescribed in the following, with the description for the secondstationary antenna 14B omitted. The first stationary antenna 12Bcomprises a modulator 28B, an oscillator 30B, a circulator 32B, adetector 36B and a microstrip antenna 34B. When an interrogatory signalis input from the control device 20B through the input pin 10Ba, themodulator 28B modulates the interrogatory signal by a carrier signalgiven from the oscillator 30B, and outputs the modulated signal throughthe circulator 32B to the microstrip antenna 34B. When a respondingsignal is received by the microstrip antenna 34B, the detector 36Bdetects the signal through the circulator 32B, and outputs it to thelevel judging circuit 22B.

The level judging circuit 22B is designed to receive responding signalsfrom both first and second stationary antennas 12B and 14B. The circuit22B judges the signal level of each responding signal received, toidentify the higher level responding signal, and sends the judgmentresult to the signal selection circuit 24B. The signal selection circuit24B is also designed to receive responding signals from both first andsecond stationary antennas 12B and 14B. Based on the judgment resultfrom the level-judging circuit 22B, the signal selection circuit 24Bselects the higher level responding signal, and outputs it to thecontrol device 20B through the demodulator 26B and the output pin 10Bb.

The control device 20B controls commands to be output from theinterrogator 10B to the responder 18B, and the operation time of theinterrogator 10B. In addition, the control device 20B processes datareceived from the responder 18B, and outputs processed data to a hostcomputer (not shown) or a display unit (not shown) as necessary.

FIG. 8 shows the construction of the responder 18B. The interrogatorysignal received by a mobile antenna 40B is input through a detector 42Bto a control unit 38B. The mobile antenna 40B is composed of amicrostrip antenna. The control unit 38B outputs a responding signal inreply to the interrogatory signal to the microstrip antenna 40B througha modulator 44B which modulates the responding signal. In addition, thecontrol unit 38B interchanges data with a data memory 46B. Eachcomponent of the responder 18B is fed with power by a battery 48B.

Now, the operation of the second invention, having the above-mentionedconstruction, will be described.

The control device 20B outputs interrogatory signals intermittently tothe interrogator 10B, so that the first and second stationary antennas12B and 14B transmit the interrogatory signals.

When the mobile object 16B enters the communication area of the firststationary antenna 12B, the responder 18B attached to the mobile object16B receives an interrogatory signal through the mobile antenna 40B. Theresponder 18B then transmits a responding signal, indicating its ownidentification number, through the mobile antenna 40B. The firststationary antenna 12B of the interrogator 10B receives the respondingsignal, and outputs it through the detector 36B to the level judgingcircuit 22B.

At this time, the responding signal from the responder 18B is alsoreceived by the second stationary antenna 14B and input to the leveljudging circuit 22B. However, the responding signal from the secondstationary antenna 14B has lower signal level than the responding signalfrom the first stationary antenna 12B. Accordingly, the level judgingcircuit 22B reckons that the responding signal input from the firststationary antenna 12B is higher, and outputs this result to the signalselection circuit 24B. Based on this result, the signal selectioncircuit 24B selects the responding signal from the first stationaryantenna 12B, and outputs it to the demodulator 26B. The demodulator 26Bdemodulates the responding signal to obtain the identification number,and outputs it to the control device 20B.

The control device 20B checks if the identification number isappropriate. If it is, the control device 20B outputs an interrogatorysignal containing a data write command or a data read command throughthe first and second stationary antennas 12B and 14B to communicate withthe responder 18B.

The signal level of the responding signal received by the firststationary antenna 12B and input to the control device 20B changes asthe mobile object 16B moves. FIG. 10A shows this change in the signallevel.

As the mobile object 16B moves and enters the overlapping zone of thecommunication areas of the first and second stationary antennas 12B and14B, the signal level of the responding signal from the secondstationary antenna 14B becomes higher than that from the firststationary antenna 12B (at the timing indicated by "A") as shown by FIG.10B. Then, the signal selection circuit 24B selects as shown by FIG. 10Cthe responding signal received from the second stationary antenna 14B,according to the instruction given by the level judging circuit 22B, andoutputs the signal to the control device 20B. Accordingly, after thetiming "A," the control device 20B controls data communication based onthe responding signal from the second stationary antenna 14B.

According to this invention, as mentioned above, the level judgingcircuit 22B and signal selection circuit 24B enable the interrogator 10Bto output to the control device 20B the higher level responding signalof the two signals received by the first and second stationary antennas12B and 14B. Therefore, although the responding signals received by thefirst and second stationary antennas 12B and 14B change as the mobileobject 16B moves, the control device 20B always receives the higherlevel responding signal.

Thus, unlike the conventional communication system in which a controldevice is provided with a means for selecting one of several stationaryantennas, the control device 20B of the communication system accordingto the present invention does not contain an antenna-switching means.Consequently, communication between the interrogator 10B and theresponder 18B can never be interrupted by an antenna-switchingoperation.

Before the mobile object identification equipment of the third inventionis explained, the conventional art as opposed to the third invention andtheir problems will be described in detail in the following.

The mobile object identification system has many applications, one ofwhich is for unmanned trucks in a factory. This system comprises a tagunit mounted as a responding unit on each unmanned truck, and antennaunits installed along the route of .unmanned trucks to provide areas forcommunication with tag units. The tag unit of this system includes amemory to store various data, such as the identification code,quantities and destination of the articles being transported by theunmanned truck. This memory is designed to allow the stored data to beread, and new data to be written as necessary.

Each antenna unit is designed to transmit a carrier wave of a specifiedfrequency as modulated by an interrogatory signal, and then anunmodulated carrier wave to its communication area. When an unmannedtruck enters the communication area, the tag unit attached to the truckreceives an interrogatory signal. The tag unit then generates aresponding signal for various data, such as the article identificationcode, to answer the interrogatory signal, modulates the unmodulatedcarrier wave received following the interrogatory signal, using theresponding signal, and transmits the responding signal-modulated carrierwave.

The antenna unit receives the responding signal, which enables the unitto identify the tag unit of the unmanned truck passing through itscommunication area, determine the articles being carried by the truck,store new data and/or control unmanned truck operation.

If unmanned trucks are allowed to move in a large area, it is necessaryto set a wide communication area to cover the large moving area. In theconventional art, this requirement is met by dividing the widecommunication area into blocks and installing a plurality of antennaunits to cover the blocks.

However, if the antenna units 10C and 12C are arranged so that thecommunication areas 14C and 16C overlap, as shown in FIG. 18, waveinterference can occur. Specifically, if an unmanned truck 20C entersthe overlapping zone 18C (in the direction indicated by the arrow), thetag unit 22C attached to the unmanned truck 20C will receive twointerrogatory signals transmitted from the antenna units 10C and 12C. Insuch a case, the two signals interfere with each other, possiblydisabling the tag unit 22C for communication.

To avoid this problem, the antenna units 10C and 12C may be arranged sothat the communication areas 14C and 16C do not overlap, as shown inFIG. 19. However, this arrangement forms a dead zone for communicationbetween communication areas 14C and 16C. If an unmanned truck 20C entersthis dead zone, the tag unit 22C of the truck 20C will not be able tocommunicate through either of the antenna units 10C and 12C.

The invention disclosed in the Japanese Patent Provisional PublicationNo. 93390/1990 solves these problems by the following method. When awide communication area is to be covered by a plurality of antennaunits, the antenna units are allocated different communication periods.As a result, if the antenna units are arranged so that theircommunication areas overlap, tag units can communicate through theantenna units without wave interference.

However, when different communication periods are allocated to each ofthe several antenna units, that is, when the communication period istime-shared by the antenna units, each antenna unit can be used forcommunication only during the allocated period. If the system involves alarge number of antenna units, the cycle of the communication period foreach antenna unit will be long. For the tag unit of an unmanned truck tocommunicate properly while it is running in the communication area, ashort communication period must be allocated to each antenna unit, orthe unmanned truck must be driven at a limited speed.

The third invention has solved the above problems. An embodiment of thethird invention will be described in detail below, with reference toFIGS. 11 through 17. In this embodiment, the third invention is appliedto the identification system for unmanned trucks.

In FIG. 12, showing the general appearance of the third invention, themotion of an unmanned truck 30C as a mobile object is controlled along aspecified runway 32C. A gate 34C is located at the specified position ofthe runway 32C, to identify each unmanned truck 30C.

The gate 34C is installed astride the runway 32C, and has a plurality ofantenna units, e.g., five antenna units 36Ca through 36Ce, in portionsabove the runway 32C. The five antenna units 36Ca through 36Ce providecommunication areas 38Ca through 38Ce, respectively, obliquely downwardto the runway 32C. Of the communication areas 38Ca through 38Ce, theadjacent ones overlap each other as shown in FIG. 11, which explains thegeneral concept of the third invention. The overlapping zones aredenoted 40Ca, 40Cb, 40Cc and 40Cd, respectively.

Referring to FIG. 11, the antenna units 36Ca through 36Ce are connectedto a controller 42C. The controller 42C not only controls datatransmission/reception of the antenna units 36Ca through 36Ce but alsosends communication data to and receives such data from a signalprocessor 44C, which may be a host computer. Each unmanned truck 30C hasa tag unit 46C as a responding unit storing various data. When anunmanned truck 30C passes through the gate 34C, this tag unit 46Ccommunicates with one of the antenna units 36Ca through 36Ce, as will bedescribed later.

FIG. 13 shows the electrical construction of the invention. Theconstruction of the antenna unit 36Ca is described. The antenna unit36Ca comprises an antenna 48C for transmitting/receiving signals, amodulation circuit 50C, an oscillator 52C, a circulator 54C, a mixer58C, and a reception circuit 56C.

The antenna 48C is composed of batch antennas realized by microstriplines formed on PC boards; these batch antennas are arranged inmultiples to form an array antenna for improving directivity and toaccommodate long-distance communication.

The modulation circuit 50C modulates carrier wave with a frequency of f1(generated by the oscillator 52C) by an interrogatory signal from thecontroller 42C, and outputs the modulated signal to the antenna 48Cthrough the circulator 54C. A specified frequency band of, e.g., 2.45GHz is allocated for the system of this invention so thatsemi-microwaves in this frequency band are output as carrier waves. Theoscillator 52C outputs semi-microwaves at a frequency of f1 in thisfrequency band. The antenna 48C is adapted to selectively receive onlyradio waves with a limited frequency of f1 set by the oscillator 52C.

The reception circuit 56, which carries out signal processing such asdemodulation, is connected to the mixer 58C. The mixer 58C receives notonly carrier waves from the oscillator 52C but also radio waves asopposed to a responding signal from the antenna 48C through thecirculator 54C. The carrier and radio waves as opposed to a respondingsignal are synthesized by the mixer 58C and input to the receptioncircuit 56C where the synthesized signal is demodulated to obtain aresponding signal. The demodulated responding signal is output to thecontroller 42C.

The antenna units 36Cb through 36Ce are the same in construction as theantenna unit 36Ca, except that the oscillation frequency of theoscillator 52C is different in each antenna unit. Specifically, whilethe oscillation frequency of the oscillator 52C for the antenna unit36Ca is set at f1, the oscillators 52C for the antenna units 36Cbthrough 36Ce are allocated narrow frequency bands which do not overlap,as denoted by f2 through f5 in FIG. 14. All these frequencies f1 throughf5 are within the specified frequency band mentioned earlier, and areallocated to the antenna units 36Ca through 36Ce so that the oscillationfrequency for an antenna unit is as different as possible from those forthe adjacent antenna units, as shown in FIG. 14.

In the controller 42C, a unit control circuit 60C is connected to themodulation circuit 50C and reception circuit 56C of each of the antennaunits 36Ca through 36Ce, to output interrogatory signals at a specifiedtiming mentioned later, and to receive responding signals. The unitcontrol circuit 60C is connected to the signal processor 44C through aninterface circuit 62C. A power circuit 64C is fed with power from an ACpower supply (not shown). When power is supplied, the power circuit 64Cconverts it to a specified DC voltage, and applies the DC voltage to theunit control circuit 60C and the interface circuit 62C, as well as tothe antenna units 36Ca through 36Ce.

In the tag unit 46C as a responding unit, an antenna 66C, composed of amicrostrip antenna formed on a PC board, is capable of receiving a widefrequency range of radio waves as indicated by the broken line in FIG.14. Specifically, it is adapted to receive all interrogatory signalswith frequencies f1 through f5 output from the antenna units 36Cathrough 36Ce.

A control circuit 68C includes a CPU, ROM, RAM etc. It is designed toreceive interrogatory signals, and to output various data, including theidentification code, in the form of responding signals to theinterrogatory signals, according to the stored program. The controlcircuit 68C is connected in two ways to the antenna 66C: through atransmission circuit 70C, and through a reception circuit 72C.

The transmission circuit 70C modulates the unmodulated carrier wavereceived through the antenna 66C, by a responding signal output from thecontrol circuit 68C, and transmits the modulated wave. The receptioncircuit 72C demodulates the radio wave received through the antenna 66C,and inputs it as an interrogatory signal to the control circuit 68C. Thecontrol circuit 68C is connected to writable/readable nonvolatile memorydata memory 74C. Each circuit in the tag unit 46C is fed with power by abattery 76C.

The operation of the third invention is described below with referenceto FIGS. 15A to 15E, 16 and 17. The unit control circuit 60C of thecontroller 42C outputs interrogatory signals to the antenna units 36Cathrough 36Ce at the timings shown in FIG. 15. Specifically, it outputsinterrogatory signals to the antenna units 36Ca, 36Cc and 36Ce at thesame timing with intervals of T1 as shown in FIG. 15A, FIG. 15C and FIG.15E, and to the antenna units 36Cb and 36Cd at the same timing withintervals of T1 but later by T2 than the timing for the former threeantenna units as shown in FIGS. 15B and 15D.

In each of the antenna units 36Ca through 36Ce, the modulation circuit50C modulates the carrier wave from the oscillator 52C by aninterrogatory signal output from the controller 42C, and sends it in theform of a microwave signal through the antenna 48C to the appropriatecommunication area 38Ca through 38Ce.

In the interrogatory signal output interval T1, the period "ta" is setfor outputting an interrogatory signal, and the remaining period "tb"for outputting a responding signal. For any two adjacent antenna units,e.g., 36Ca and 36Cb, the interrogatory signal output periods "ta" do notoverlap.

The modulation circuit 50C of each antenna unit 36Ca through 36Ce doesnot carry out modulation in the period "tb" when interrogatory signalsare not given from the controller 42C. During this period, the carrierwave from the oscillator 52C is output unmodulated to each of thecommunication areas 38Ca through 38Ce via the antenna 48C. In otherwords, each antenna unit 36Ca through 36Ce always outputs radio waves,but transmits an interrogatory signal only during the period "ta" whichcomes at intervals of T1.

With interrogatory signals being thus output to the communication areas38Ca through 38Ce, when an unmanned truck 30C, approaching the gate 34Con the runway 32C, enters the communication area 38Ca, the tag unit 46Ccommunicates by the following method. The tag unit 46C receives radiowaves by the antenna 66C. The reception circuit 72C demodulates theradio waves to an interrogatory signal, and sends the signal to thecontrol circuit 68C.

Determining that the interrogatory signal is from the antenna unit 36Ca,the control circuit 68C outputs a responding signal of theidentification code to the transmission circuit 70C. At this time, theantenna 66C is receiving an unmodulated carrier wave from the antennaunit 36Ca, and is sending it to the transmission circuit 70C. Thetransmission circuit 70C modulates this carrier wave by the respondingsignal, and reflects the modulated carrier back for transmission.

The antenna unit 36Ca receives the responding signal radio wave throughthe antenna 48C, thereby identifying the tag unit 46C. Morespecifically, the radio wave received by the antenna 48C is inputthrough the circulator 54C and the mixer 58C to the reception circuit56C, where it is demodulated to the responding signal and sent to thecontroller 42C. The unit control circuit 60C of the controller 42C theninputs the identification code data of the communicating tag unit 46Cthrough the interface circuit 62C to the signal processor 44C.

To continue communicating with the tag unit 46C, the controller 42Ccontrols the antenna unit 36Ca to output an interrogatory signal duringthe next interrogatory signal output period. If the interrogatory signalincludes a write command instructing the tag unit 46C to store certaindata, the control circuit 68C of the tag unit 46C carries out theprocessing to write the data to the data memory 74C. If theinterrogatory signal includes a read command instructing the tag unit46C to read certain data, the control circuit 68C of the tag unit 46Ccarries out the processing to read the data from the data memory 74C,and output it for communication.

Now the operation of the present invention is described for the case inwhich the tag unit 46C of an unmanned truck 30C passes through theoverlapping zone 40Cc, between the communication area 38Cc of theantenna unit 36Cc and the communication area 38Cd of the antenna unit336Cd, as shown in FIG. 16. Since the interrogatory signal output timingof the antenna unit 36Cd lags by T2 behind that of the antenna unit 36Ccas described earlier, the tag unit 46C in the overlapping communicationzone 40Cc receives the radio wave of an interrogatory signal from eitherthe antenna unit 36Cc or 36Cd.

The tag unit 46C may receive the radio wave of an interrogatory signalfrom the antenna unit 36Cc first. The control circuit 68C of the tagunit 46C accepts the signal, and outputs a responding signal accordingto the process described above. The transmission circuit 70C modulates,by responding signal, the unmodulated carrier wave received from theantenna unit 36Cc through the antenna 66C, and reflects it back fortransmission. At the time of responding signal transmission, the antenna66C may receive an interrogatory signal radio wave from the antenna unit36Cd because the tag unit 46C is positioned in the overlappingcommunication zone 40Cc.

In such a case, the responding signal radio wave being transmitted fromthe antenna 66C to the antenna unit 36Cc is also transmitted to theantenna unit 36Cd, and the interrogatory signal from the antenna unit36Cd is modulated by a responding signal and transmitted to both antennaunits 36Cc and 36Cd. However, since the frequencies of radio wavestransmitted from the antenna units 36Cc and 36Cd are set differently atf3 and f4, respectively, the antenna unit 36Cc can receive and identifythe radio wave of responding-signal modulated carrier waves with afrequency of f3 alone. Furthermore, by including the identification codefor each of the antenna units 36Ca through 36Ce in each interrogatorysignal, and that for each tag unit 46C in each responding signal, eachantenna or tag unit that receives a signal can determine whether thesignal is intended for that antenna unit.

Thus, the tag unit 46C responds only to the interrogatory signal fromthe antenna unit 36Cc--the signal received first --, communicating withthe antenna unit 36Cc. After completing communication with the antennaunit 36Cc, if the tag unit 46C remains in the overlapping zone 40Cc, itwill accept the interrogatory signal from the antenna unit 36Cd andcommunicate with it. Therefore, the tag unit 46C can communicate withthe antenna units 36Cc and 36Cd accurately, without radio interferencebetween the antenna units.

Furthermore, since the communication time is not divided between theantenna units 36Cc and 36Cd as it is for conventional time-sharingcommunication, each antenna unit is not limited in communication time.Consequently, even when the unmanned truck 30C is moving at high speedin the overlapping communication zone 40Cc, the tag unit 46C hassufficient communication time to be identified by the antenna unit 36Ccor 36Cd.

In the overlapping communication zone 40Cc, the tag unit 46Ccommunicates with both antenna units 36Cc and 36Cd, and upon completingcommunication with either of the antenna units, it stops communicatingwith the other unit. Accordingly, when the unmanned truck 30C is movingon the runway 32C, passing through the communication area 38Cc, theoverlapping zone 40Cc and the communication area 38Cd, in the directionindicated by the arrow in FIG. 17, the tag unit 46C keeps communicatingwith both antenna units 36Cc and 36Cd, without interruption due tochange in the communication area. By maintaining communication with bothantenna units 36Cc and 36Cd, the tag unit 46C can always exchangesignals with either of the antenna units 36Cc and 36Cd until itcompletes communication. When completing communication with either ofthe antenna units 36Cc and 36Cd, the tag unit 46C stops communicatingwith the other antenna unit 36Cc or 36Cd, as mentioned earlier, toprevent duplicate data writing; if duplicate data writing is notanticipated, it is not necessary to stop communicating with the otherantenna unit.

Thus, according to the above embodiment of the third invention, whilethe five antenna units 36Ca through 36Ce, providing communication areas38Ca through 38Ce, respectively, are set with the communication areas ofthe adjacent antenna units overlapping, the oscillators 52C of the fiveantenna units 36Ca through 36Ce are allocated with different narrowbands of oscillation frequencies f1 through f5, and the controller 42Ccontrols the antenna units 36Ca through 36Ce so that adjacent antennaunits provide overlapping communication zones 40Ca through 40Cd outputinterrogatory signals at different timings, with the time lag T2. As aresult, each of the antenna units 36Ca through 36Ce can communicateaccurately and promptly with the tag unit 46C of an unmanned truck 30Cpassing through the respective communication areas.

In the above embodiment, the antenna units 36Ca through 36Ce arepositioned so that the communication areas of adjacent antenna unitsoverlap. Alternatively, the antenna units 36Ca through 36Ce may bepositioned so that the communication areas of three or more of theantenna units overlap. In such a case as well, communication can beaccurate, without any radio interference, if the antenna units 36Cathrough 36Ce are controlled to output interrogatory signals at differenttimings.

In the above embodiment, the third invention is applied to an unmannedtruck identification system. The invention is applicable to other mobileobject identification system as well, including factory process controlsystem for control of products in the production line, and in systemsfor managing room entry/exit.

Before the fourth and fifth inventions are explained, the conventionalarts as opposed to the fourth and fifth inventions and their problemswill be detailed in the following.

Presently, a vehicle is identified from the exterior by the licenseplates attached to its front and rear (or to the rear alone for atwo-wheeled vehicles), from the mandatory vehicle inspection label to beupdated three years after purchase and thereafter every two years ingeneral, and from the regular inspection and maintenance labelindicating that the vehicle has undergone regular inspection andmaintenance. These labels are often attached to the inside of the frontwindshield. All of the above information for identifying the vehicle ischecked visually. When a vehicle is moving, it is difficult to check theabove information visually, particularly at night.

A non-contact information card is conventionally known as means forradio communication. When this information card is used in a vehicle,the driver holds up the card to face it toward an interrogator or otherinformation reader, or places it on the dashboard, to communicate withthe interrogator. If this information card retains vehicleidentification data such as the frame number stamped on the frame ofeach vehicle, the vehicle registration number shown on the licenseplate, and the expiration date of the mandatory inspection certificate,the information card could be used to provide the identifyinginformation specific to each vehicle.

In such applications, however, since the information card is not fixedto the vehicle, it can be taken and used for other vehicles.Consequently, the information stored in the information card does notalways conform to the identifying information specific to the vehiclefor which the card is being used. Such information card is therefore notpractical in view of its high potential for abuse.

The fourth invention has solved the above problem. An embodiment of thefourth invention is described below. FIG. 20 is a general view of theelectronic mandatory inspection label 1D according to an embodiment ofthe fourth invention. The electronic mandatory inspection label 1D isroughly divided into a visible information layer 2Da and an electroniccircuitry layer 2Db, which are joined with adhesive so as not to beeasily separable. The visible information layer 2Da may be made ofpaper, with printed information, including a figure indicating the monthof expiration of the mandatory inspection certificate. The electroniccircuitry layer 2Db incorporates a responding circuit 3D which sends andreceives electronic information.

The electronic mandatory inspection label 1D is fixed to the frontwindshield 7Da of a vehicle 7D, as shown in FIG. 21, using adhesive sothat it cannot be removed, or using an appropriate change-preventivematerial that leaves clear evidence of removal. The electronic mandatoryinspection label 1D communicates with interrogators 8D (described later)installed along a road.

The most preferable fixing position of the electronic mandatoryinspection label 1D is, as shown in FIG. 21, the upper center of thefront windshield 7Da, just behind the rearview mirror RM, as viewed fromthe driver's seat. In this position, the label does not obstruct thedriver's view. In addition, this position is outside the moving range(indicated by the chain double-dashed lines in FIG. 21) of thewindshield wiper arms WP, so that the metal used in the wiper arms hasminimal influence on communication between the responding circuit 3D andan interrogator 8D.

The construction of the responding circuit 3D is now described indetail, with reference to FIG. 22. The responding circuit 3D comprisesan IC chip 21D for processing internal information, an antenna 22D forreceiving interrogatory signals S1 and transmitting responding signalsS2, and a built-in battery 23D for driving the IC chip 21D.

The IC chip 21D comprises a detector 21Da, a level comparator 21Db, amemory 21Dc, a central processing unit (hereinafter referred to as theCPU) 21Dd, a clock generator 21De, and a modulator 21Df. The detector21Da detects information in an interrogatory signal S1 received by theantenna 22D. The level comparator 21Db confirms reception of theinterrogatory signal based on the signal level data sent from thedetector 21Da, and supplies power to each circuit. The memory 21Dcstores vehicle information such as a frame number, data on the mandatoryinspection certificate expiration, and a vehicle registration number(license plate number). When the CPU 21Dd receives power from the levelcomparator 21Db, it transmits a signal according to the informationstored in the memory 21Dc. The clock generator 21De generates clockpulses to operate the CPU 21Dd. The modulator 21Df modulates theinterrogatory signal S1 using the signal output from the CPU 21Dd, andtransmits it as a responding signal S2 through the antenna 22D.

An interrogatory signal S1 sent from an interrogator 8D is received bythe responding circuit 3D through the antenna 22D. Receiving thissignal, the level comparator 21Db starts to supply power to the CPU 21Ddand to the clock generator 21De. Then, the CPU 21Dd interprets andexecutes the command contained in the interrogatory signal S1. If thecommand demands internally stored data, the CPU 21Dd operates tomodulate the interrogatory signal S1 by the information stored in thememory 21Dc and to transmit it as an internal-information-bearingresponding signal S2 through the antenna 22D.

Now, the following paragraphs describe an interrogator 8D which outputsradio waves to the responding circuit 3D to obtain vehicle information.

The means of the interrogator 8D is to transmit interrogatory signals S1to, and receive responding signals S2 from, the above-mentionedelectronic mandatory inspection label 1D. As shown in FIG. 23, theinterrogator 8D comprises: a carrier generation circuit 11D to generatea carrier wave; a modulator 12D to produce an interrogatory signal S1 bysuperposing information on the carrier wave; a circulator 13D toseparate transmission waves from received waves; an antenna 14D as theentrance and exit of electromagnetic waves; a demodulator 15D to detectinformation in the received waves of a responding signal S2; a signalprocessor 16D to control the modulator 12D and demodulator 15D toprocess information; and an external interface 17D which communicatesnecessary information of the received responding signal S2 to an upperinformation processing system (such as the system management computer30D shown in FIG. 25).

The signal processor 16D is composed of a CPU 16Da which includesprograms to control communication, and a system-identifying informationsetting block 16Db which sets the identification number for the system.This block 16Db is composed of a PROM 16Dc to store system-identifyinginformation.

Having the circuitry construction mentioned above, the interrogator 8Doperates as follows.

An interrogatory signal S1 to be transmitted from the interrogator 8D isproduced in the modulator 12D by modulating the carrier wave from thecarrier wave generation circuit 11D. In other words, the data sent fromthe signal processor 16D to the modulator 12D is superposed on theinterrogatory signal S1. The interrogatory signal S1 thus produced issent through the circulator 13D, and is radiated into the air throughthe antenna 14D.

When a responding signal S2 is returned from the responding circuit 3Dof the electronic mandatory inspection label 1D, the interrogator 8Dreceives it by the antenna 14D. The responding signal S2 is then inputthrough the circulator 13D to the demodulator 15D, which extractsinformation from the responding signal S2 and gives the information tothe signal processor 16D. The signal processor 16D processes theinformation, and outputs it, if necessary, to the external interface17D. The signal processor 16D also carries out internal processing basedon the control instruction and various other information input from theexternal interface 17D, and sends transmission data to the modulator12D.

Using the above-mentioned electronic mandatory inspection label 1D andinterrogator 8D, it is possible to realize the systems given below:

(1) Toll road accounting system (FIG. 24)

When an ordinary vehicle B approaches a toll gate T on a toll road TR,the vehicle B is required to run along the first lane R1 and stop infront of the toll booth 27D to pay the toll to a collecting person P.

Meanwhile, when a vehicle A bearing the electronic mandatory inspectionlabel 1D approaches the toll gate T, it has only to run along the secondlane R2 to pay the toll; the interrogator 8D installed above the secondlane R2 reads the frame number and other vehicle information from theelectronic mandatory inspection label 1D of the vehicle A, and judgesthe vehicle A admissible to the road, based on the informationregistered in the system management computer (not shown). In this case,the toll may be paid from the designated bank account on a later day. Ifread information is stored in a database, it is possible to obtainmonthly data on how many times each vehicle has passed the toll gate T,thus enabling the system to give toll discounts to vehicles frequentlyusing the toll road.

(2) Incoming/outgoing vehicle management system of a parking lot (FIG.25)

When a vehicle C bearing the electronic mandatory inspection label 1Denters a parking lot, the interrogator 8D installed at the upper part ofthe entrance reads the frame number and other vehicle information of thevehicle C from the electronic mandatory inspection label 1D. The vehicleinformation read by the interrogator 8D is input to the systemmanagement computer 30D connected with the interrogator 8D. If the framenumber of the vehicle C has been registered as a customer of the parkinglot, the computer 30D judges the vehicle C as a customer, based on theinput information, and opens the barrier gate 32D.

The vehicle C is thus allowed to enter the parking lot without payingthe parking charge at the entrance. The charge may be paid from thedesignated bank account on a later day as in the case of the toll roadaccounting system. If read information is stored in a database, it ispossible to obtain monthly data on how many times each vehicle has usedthe parking lot, thus enabling the system to give discounts on parkingcharges to vehicles frequently using the parking lot.

(3) Regular customer sensing system (FIG. 26)

When a vehicle D bearing the electronic mandatory inspection label 1D isto enter the parking lot of a department store, the interrogator 8Dinstalled at the entrance reads the vehicle information from the label1D. If the vehicle information indicates that the visitor is a specialregular customer, the system may show a vacant parking space number onthe guideboard 41D, and inform the special customers section of thevisit of the special regular customer by displaying such on theindication board 45D, thus enabling a person in charge to meet thecustomer promptly.

(4) Illegal parking control by the police

In controlling illegal parking, the police can collect vehicleinformation (frame numbers, license plate numbers etc.) using a portablehandy terminal that incorporates the interrogator 8D. This tooleliminates the need to fill out documents with pens, allowing eachpoliceman to control a large number of illegally parking vehiclesefficiently in a short period of time.

(5) Control by the police of vehicle mandatory inspection certificateexpiration

By installing the interrogator 8D above or on the side of roads, thepolice can control vehicles whose mandatory inspection certificates haveexpired. With radio waves transmitted to each oncoming vehicle, theinterrogator 8D reads at least the frame number and the expiration dateof the mandatory inspection certificate from the electronic mandatoryinspection label 1D attached to the vehicle. Based on the informationthus read, the police can find illegal vehicles. Conventionally, to findsuch illegal vehicles, policemen have been required to visually read themonth of expiration on each mandatory vehicle inspection label 55D (FIG.27). The present application of the fourth invention relieves policemenfrom such troublesome and inefficient work, and is very effectivebecause it enables the police to obtain vehicle information easily, evenfrom a moving vehicle.

(6) Criminal investigation by the police

In criminal investigation, the police may be required to detect anescaping vehicle. The electronic mandatory inspection label 1D can beapplied to this purpose. In such application, the interrogators 8D areinstalled at important points of cities, so that information on theescaping vehicle can be obtained and referred to for pursuit.Conventionally, investigators have been required to identify visuallythe characteristic and license plate number of the escaping vehicle. Thepresent invention eliminates the need for such visual identification,and is very effective because it enables the police to identify thevehicle in question easily, even if the vehicle is moving.

The electronic label for a vehicle according to the fifth invention isdescribed in the following.

FIG. 27 is a general view of the front windshield 51D, as viewed frominside the vehicle, which incorporates the responding circuit 53D of theelectronic label for a vehicle according an embodiment of the fifthinvention. The responding circuit 53D is integral with a power line 57D,and is embedded in the front windshield 51D. The power line 57D ispassed through the front windshield 51D, and connected to an on-boardbattery 59D.

The responding circuit 53D is embedded in the front windshield 51D at aposition, for example, behind the rearview mirror RM, where themandatory vehicle inspection label 55D is attached. Concealed by themirror RM and the mandatory vehicle inspection label 55D, the respondingcircuit 53D is not visible from the driver's seat. Preferably, theresponding circuit 53D is located in the upper center of the frontwindshield 51D and outside the moving range (indicated by the chaindouble-dashed lines in FIG. 27) of the windshield wiper arms WP, for thesame reason as mentioned for the electronic mandatory inspection label1D of the fourth invention.

More preferably, the mandatory vehicle inspection label 55D should beattached to the front windshield 51D in such a position that the upperend portion of the label 55D is laid over the responding circuit 53D, sothat the necessary information, including the figure indicating theexpiring month on the label 55D is visible, and that the respondingcircuit 53D is hidden behind the label 55D.

The responding circuit 53D of the fifth invention is of the sameconstruction as the responding circuit 3D of the electronic mandatoryinspection label 1D, except that the former circuit 53D does not have abuilt-in battery 23D. Specifically, as shown in FIG. 28, it comprises anantenna unit 61D for transmitting and receiving radio waves, an IC chip62D for processing internal information, and a power line 57D forsupplying power to drive the IC chip 62D, all arranged on a transparentPET substrate 60D.

FIG. 29 shows another general view of the front windshield 51D, asviewed from the inside of a vehicle, in which the responding circuit 53Dis connected to another information processor 70D, which may be an ICcard reader/writer. In this case, as shown, the responding circuit 53Dis integrally connected with a communication/power line 57D, and isembedded in the front windshield 51D. The communication/power line 77Dis passed through the front windshield 51D and connected to theinformation processor 70D, which is connected to the on-board battery59D. An IC card, a floppy disc, a reloadable optical disc (compactdisc), or any other reloadable tool may be used as informationprocessing media for the information processor 70D.

Some methods of embedding the responding circuit 53D in the frontwindshield 51D will be described with reference to FIGS. 30A to 30C.FIGS. 30A and 30B show a method applicable when the front windshield isof laminated glass. In the process of manufacturing the laminated glass,the responding circuit 53D is sandwiched together with a resin sheet51Db between a top glass sheet 51Da and a bottom glass sheet 51Dc. FIG.30C shows another method. A recess is formed inside the front windshield51D, and the power line 57D or communication/power line 77D is passedthrough the glass to a position under the recess. Then, the respondingcircuit 53D is set in the recess so that the electrodes of the circuit53D come in contact with the power line 57D or communication/power line77D. A glass cover 51Dd is placed over the responding circuit 53D, andfixed to the front windshield 51D using adhesive 51De. By either of theabove methods, it is possible to integrally incorporate the respondingcircuit 53D into the front windshield 51D (or in other words, into avehicle body).

If the responding circuit 53D of the fifth invention incorporated intothe front windshield 51D is mounted on a vehicle, it is also veryeffectively applicable to the toll road accounting system, theincoming/outgoing vehicles management system of a parking lot, theregular customer sensing system, the control by police of illegalparking or expiration of the vehicle mandatory inspection certificate,criminal investigation by the police etc., as is the electronicmandatory inspection label 1D of the fourth invention.

The operation of the fifth invention in application as a toll accountingsystem of FIG. 24 is described in the following. If the respondingcircuit 53D is connected to an IC card reader/writer as the informationprocessor 70D, as shown in FIG. 29, and if the IC card has a prepaidmeans, the information that the vehicle A has been judged admissible tothe toll road is sent through the communication/power line 77D to the ICcard reader. The IC card then deducts one point from the number ofprepaid points, thereby paying the toll. If the IC card has a creditmeans, after vehicle A has been judged admissible, the credit number isoutput from the IC card to the responding circuit 53D. The respondingcircuit 53D communicates the credit number to the interrogator 8D, topay the toll on credit.

In the application to the incoming/outgoing vehicle management system ofa parking of FIG. 25 as well, if the responding circuit 53D is connectedwith the IC card reader/writer to enable the interrogator 8D to read thecredit number, the driver can pay the parking charge on credit.

In the embodiment described above, the responding circuit 53D is locatedin the position where the vehicle mandatory inspection label 55D isattached, as shown in FIG. 27. The responding circuit 53D may bepositioned in the upper left corner of the front windshield 51D, wherethe regular check and maintenance label 56D is attached as shown in FIG.27. In this position as well, the responding circuit 53D is outside themoving range (indicated by the chain double-dashed lines in FIG. 27) ofthe windshield wiper arms WP.

In the present embodiment of the fifth invention, the responding circuit53D is embedded in the front windshield, for convenience incommunicating with an interrogator 8D and on the assumption thatvehicles normally move forward. The responding circuit 53D can beembedded in the rear windshield or a window glass without affecting thespirit of the invention. However, considering that the invention isapplied to various police control systems, as mentioned above, theresponding circuit 53D should not be built into movable window glass forthe following reason: if the window glass containing the respondingcircuit 53D has been moved into the side panel to open the window, themetal of the side panel hampers communication between the respondingcircuit 53D and the interrogator 8D.

According to the present embodiment of the fifth invention, transparentPET is used for the substrate of the responding circuit 53D, as shown inFIG. 28. Other material, such as resin and glass, may be used instead ofPET as long as it is transparent.

Now, a second embodiment of the fifth invention concerning theresponding-circuit-incorporating windshield 51D is described in thefollowing. FIG. 31 shows the electrical construction of the secondembodiment. As shown, the second embodiment comprises an antenna 101D,an information processor 104D, a shield wire 107D connecting the antenna101D with the information processor 104D, a power supply 106D, and anactuator 105D. The information processor 104D is composed of an RFprocessing IC 102D and a reader/writer (hereinafter referred to as R/W)103D which exchanges data with the RF processing IC 102D.

The R/W 103D may be an IC card R/W or a magnetic card R/W. For theshield wire 107D, a shielded wire, not an ordinary wire, is used toprotect the system from noise generated between the antenna 101D and theRF processing IC 102D. The actuator 105D is, for example, a driver'sseat position adjusting motor, or a door-mirror angle adjusting motor.

More specifically, the antenna 101D is embedded in the front windshield111D at a position behind the rearview mirror RM, where the mandatoryvehicle inspection label 55D is attached, or at a position where theregular check and maintenance label 56D is attached, so that it does notobstruct the driver's view, as shown in FIG. 32. The antenna 101D isconnected to the information processor 104D housed in the dashboard, bythe shield wire 107D laid around the front windshield 111D.

As shown in FIG. 33, the RF processing IC 102D of the informationprocessor 104D includes two different memories 113D: an EEPROM 114Dwhose data can be rewritten electrically but cannot be erased or changedby ON/OFF of power supply or by ultraviolet ray radiation; and an SRAM115D whose data can be reset (erased) by ON/OFF of power supply. Theidentifying information specific to a vehicle, such as the license platenumber, and the expiration date of the mandatory inspection certificate,is stored in the EEPROM 114D. Information on an individual person suchas the person's identification number for a membership athletic club;and the registration number for the toll road accounting system of FIG.24 or for a particular parking space of the incoming/outgoing vehiclemanagement system of a parking lot (FIG. 25) is stored in either theSRAM 115D or the EEPROM 114D. The information processor 104D is equippedwith a ten-key board so that individual information can be called fromthe EEPROM 114D by inputting the appropriate code number.

The operation of the second embodiment of the fifth invention isdescribed in the following.

When the relevant vehicle is registered, the vehicle registrationnumber, the expiration date of the mandatory inspection certificate andother data specific to the vehicle are input to the EEPROM 114D of theRF processing IC 102D. Such data can be input to the EEPROM 114D throughthe R/W 103D by using an IC card or a magnetic card, or through theantenna 101D embedded in the front windshield 111D by sending radiowaves to the antenna 101D. The data thus input can be changed only byofficials of the Land Transportation Bureau at the time of vehiclemandatory inspection or reregistration, and cannot be changed by otherindividuals.

Prior to using the vehicle for the first time, the driver is expected toinput the individual information to the EEPROM 114D of the memory 113D,by inserting an IC card or magnetic card into the information processor104D (R/W 103D) housed in the dashboard. At that time, the driver isalso expected to register code numbers. The individual information thusstored is not erased by turning the power supply or the engine on oroff, and can be called up as desired by inputting the appropriate codenumber. Accordingly, the driver need not carry his/her IC card ormagnetic card. In addition, it is not necessary for the driver to inputthe individual information each time the vehicle is used.

In actual operation, when the vehicle engine is started, thevehicle-specific information stored in the EEPROM 114D, that is, thelicense plate number and the expiration date of the mandatory inspectioncertificate, are unconditionally input to the SRAM 115D. When a codenumber is input, the individual information as opposed to the codenumber is also uploaded. As the vehicle in this state is passing infront of the interrogator 8D of the system shown in FIG. 24 or 25, theinterrogator 8D receives the information stored in the SRAM 115D fromthe antenna 101D embedded in the vehicle.

The information received by the interrogator 8D is input to the hostcomputer (not shown) of the system for necessary processing. When theinterrogator 8D transmits information, it is received by the antenna101D of the vehicle, and written in the EEPROM 114D of the informationprocessor 104D when necessary.

When the engine is stopped, the power supply 106D is turned off, and theinformation in the SRAM 115D of the RF processing IC 102D is erasedwhile the information stored in the EEPROM 114D remains unerased.

In the above second embodiment of the fifth invention, the RF processingIC 102D is installed in the information processor 104D housed in thedashboard. Alternatively, it may be embedded together with the antenna101D in the front windshield 111D. In that case, the shield wire 107D isnot necessary.

In the above second embodiment, code numbers are used to call upindividual information. Other means, such as a magnetic card, IC card,and collation of fingerprints, may be used to this end, as long as itenables the driver to confirm the information specific to the vehicle.

In the above second embodiment, the antenna 101D is embedded in thefront windshield 111D. It may be attached to the inside of the frontwindshield 111D. The information processor 104D may be equipped with adisplay to show the content of communication. The R/W 103D may be anoptical card R/W instead of an IC or magnetic card R/W.

The embodiments of the first through the fifth inventions have beendescribed independently in the above paragraphs. Needless to say, themobile object identification system is realized by combining the firstthrough the fifth inventions.

INDUSTRIAL APPLICABILITY OF THE INVENTION

According to the first invention, as described above, if the responderfor the mobile object identification system receives a write signal froma writing interrogator, with the write completion status stored, thecontrol means invalidates the write signal. Consequently, the responderwrites data only once as it passes through the communication area of thewriting interrogator. Thus, despite its simple construction, the firstinvention is effective in preventing duplicate data writing.

According to the second invention, the interrogator of the communicationcomplex for the mobile object identification system includes a leveljudging circuit to identify the highest level responding signal of thosereceived by the stationary antenna, and a signal selection circuit toselectively output to the control device the responding signalidentified by the level judging circuit. With the communication complexaccording to the second invention, therefore, it is not necessary toswitch over the multiple antennas of the interrogator to communicatewith the responder. In other words, the second invention provides such asuperior effect that it allows the responder to complete communicatingwith the interrogator without interruption.

With the mobile object identification equipment according to the thirdinvention, the control means controls the plurality of interrogators sothat at least those interrogators whose communication areas overlapprovide different-frequency carrier waves and transmit interrogatorysignals at different timings. Therefore, even in the overlapping zone ofcommunication areas, there is no need to divide interrogator outputsignals communication time, and there is no possibility that theresponder receives two interrogatory signals at a time. Thus, the thirdinvention provides such superior effects that it prevents radiointerference and promises accurate and prompt communication even whenthe responder is moving at high speed.

When the electronic label for the mobile object identification systemaccording to the fourth or fifth invention is attached to or embedded ina vehicle, and when an interrogatory signal is sent from an externalinterrogator to the vehicle, the responding circuit receives theinterrogatory signal and sends back appropriate vehicle informationstored in advance in the responding circuit. Therefore, it is notnecessary for persons to identify vehicle information visually. Inaddition, the vehicle information can be identified easily even when thevehicle is moving. If the electronic label bears on its surface theinformation provided on the particular labels legally required to beattached to the front windshield of a vehicle, the electronic label canbe attached to the front windshield without causing any problems. Aswell, the electronic label bearing such information on the surface isnot expected to be removed from the vehicle. Accordingly, theinformation read from the electronic label may be reasonably consideredas information specific to the vehicle.

Thus, with the electronic label according to the fourth or fifthinvention, the vehicle-related information, such as the frame number andthe expiration date of the mandatory inspection certificate, can becollected by the interrogator by non-contact means, and not visually.Therefore, the fourth or fifth invention is extremely effective ifapplied to the toll or parking charge collecting system, illegal vehicleor illegal parking control by the police, criminal investigation by thepolice etc.

What is claimed is:
 1. A responder which is attached to a movable objectfor writing data when receiving a write signal in a communication areaof a writing interrogator and reading and transmitting data whenreceiving a read signal in said communication area of a readinginterrogator, as said responder is moved with said movable object, saidresponder comprising:data storage means for storing data; control meansfor controlling a process of writing data into said storage means, andfor controlling a process of reading data from said data storage means;and status storage means for storing write completion status data whensaid control means controls said process of writing data to said datastorage means in response to a first write signal from said writinginterrogator; said control means invalidating said process of writingdata to said data storage means when said control means receives asecond write signal from said writing interrogator.
 2. A communicationsystem for a mobile object identification system, comprising:a respondertransmitting and receiving signals through a mobile antenna mounted on amobile object; an interrogator transmitting and receiving signalsthrough a plurality of stationary antennas installed along a moving areaof said mobile object, said plurality of stationary antennas havingrespective communication areas which overlap partly in a direction ofmovement of said mobile object; and a control device controlling anoperation of said interrogator; wherein said interrogator includes leveljudging and signal selecting means for simultaneously judging respectivesignal levels of a plurality of responding signals received respectivelyby said plurality of stationary antennas, for selecting one of saidplurality of responding signals, and for outputting said selected one ofsaid plurality of responding signals.
 3. A mobile object identificationsystem, comprising:a responder mounted on a mobile object and which,when receiving an interrogatory signal with a first frequency, modulatesby a responding signal an unmodulated carrier wave received after saidinterrogatory signal, and which transmits saidresponding-signal-modulated carrier wave; a plurality of interrogators,each of said plurality of interrogators modulating a respective carrierwave having a predetermined frequency allocated for respectiveoverlapping communication areas of each of said plurality ofinterrogators by a respective interrogatory signal, each of saidplurality of interrogators transmitting said modulated carrier wave,followed by an unmodulated carrier wave, to said respectivecommunication area, adjacent ones of said respective communication areasof said plurality of interrogators having different carrier frequencies,and each of said plurality of interrogators receiving a respondingsignal from said responder when positioned in said respectivecommunication area; and control means for controlling said plurality ofinterrogators so that said adjacent ones of said plurality ofinterrogators transmit said respective interrogatory signals atdifferent times.
 4. An electronic label for a mobile objectidentification system, comprising:a responding circuit for storingvehicle information varying from vehicle to vehicle, said respondingcircuit outputting said vehicle information in response to aninterrogatory signal received from an interrogator; and a visualinformation sheet attached on a windshield glass of a vehicle to facesaid responding circuit, said visual information sheet being displayedon said vehicle so as to be seen from an exterior of said vehicle;wherein at least said responding circuit is embedded in said windshieldglass of said vehicle.
 5. An electronic label for a mobile objectidentification system, comprising:a responding circuit which is embeddedin a windshield glass of a vehicle, said responding circuit storingvehicle information varying from vehicle to vehicle, and said respondingcircuit outputting said vehicle information in response to aninterrogatory signal received from an interrogator; said respondingcircuit being placed just above a rear view mirror of said vehicle andconnected to a battery of said vehicle through a power line.
 6. Aresponder according to claim 1, wherein said control means invalidatessaid process of writing data to said data storage means when saidcontrol means receives a second write signal from said writinginterrogator and said write completion status data retained in saidstatus storage means indicates that said control means allowed data inresponse to said first write signal to be written to said data storagemeans.